Solar Thermal notes

Notes whilst gearing up to install a solar thermal system in Summer
2011:

Solar Notes {#internal-source-marker_0.4253682322397573 dir=”ltr”}

Sizing
tank and panel: allow 5.5 - 8.5 Litres of water per solar tube
(30tubes for 175-260L). May want 40 tubes given non-optimal
position and daily baths for GJ. 40 tubes at the recommended 5L per
47mm tube = 200L. “210L is over size for two of us” (but with GJ
we’ll use a lot more water). But Ken reasons that a 40tube panel
can deliver 18kWh in peak sunshine in June, which will raise 250L by
62 degrees C.

Shouldn’t
need planning permission but a good idea to get it

20
tubes = about 50 kg

need
to double-check that all the pipes can be accessed from one
side

don’t
use standard pipe insulation as it will melt about 100 degrees
C

Navitron
do courses every month and an ‘EASYMCS Scheme’ - allowing to to
subcontract under our MCS certification, so your installations will
be MCS-approved for government incentives. (Microgeneration
Certification Scheme)

divert
excess heat to radiator in airing cupboard???

measure
total energy produced

RHI

Navitron
kit is good for RHI. Domestic RHI
will start in Oct 2012. Solar heating: 8.5p/kWh

There’s
talk of an RHI
“Premium
Payment”,
a 1-off grant of £300 from July 2011. No details though. Ofgem
is responsible for paying. We’ll need to get an EPC to qualify,
and we need to provide feedback.

“DECC
have said that they will release details of the RHPP (the
premium payment ‘grant’ that will cover the first year for
domestic RHI) from w/c 7th June so probably best to wait for
that if you can.”

Some
talk of thermal stores “dying very quickly in hard water areas”.
We
are in a hard water
area
(266.0 mgl CoCO3 ppm, 18.6 Degrees Clarke, 14.9 Degrees German (DH),
26.6 Degrees Franch). <100ppm = soft, 100-200ppm=
medium, >200ppm = hard. “We also live in a very hard
water area. I use a simple phosphate water softener and have had no
furring problems anywhere in over 20 years. In fact when we first
fitted it, it cleared lots of the scale that was already there.
(link)”
(a
specific recommendation for a water
softener)
Scale can be cleared with acid flushing. Some talk of replaceable
DHW coils, although I think they may be for really large (2000L)
tanks.

Tallness
and insulation at the top are important for stratification

“Heat
Bank” (basically a normal, cheap vented cylinder which feeds a
heat exchanger.) (diagram)The
big advantage is the the heat exchanger is easily replaced (whilst
the DHW coil can’t be replaced so the whole heat store has to be
replaced, I think), which is important given our hard water. Plus I
think flow rate is higher (not sure though). Wookey:
“The point about this set-up is that hot always goes in at the top
from any source, and is extracted from the top so you can run the
system stratified and without heating up a load of water unless you
mean to. I intend to never heat more than the top 50l or so by
boiler-power.” Some talk of using “diffusers” on the inputs to
ensure inputs don’t break the tank’s stratification. Wookey:
“I found this paper last night:http://www.byg.dtu.dk/upload/institutter/byg/publications/rapporter/byg-r100.pdf
which refers to another paper (sadly in Danish) which tested
stratification with different input baffle shapes, and found that a
flat-circular nozzle is the best diffuser for stratification, with
T-pieces next then drilled-pipe diffusers, then direct holes, which
seems a bit disapointing as drilled-pipe seems to be standard. I am
quite surprised by this finding. No doubt Newark aet al will fit
T-pieces if one asks.” Stratification good because you want a low
temp (at bottom) to get max power from solar, but high temp
at top.

Sounds
like the controller should be set to heat the tank if the top of the
tank drops below 55 degrees C.

One
problem with thermal stores / heat banks is that the condensing
boiler will often receive a high return temp and so wont condense
(not sure what to do about this though)

Perhaps
consider running the bathroom UFH from the hot water tank. One
possibility would be to use the UFH circuit as the heat dump.

“The
pump you require is a bronze bodied type (rather than the cast
iron standard). Look athttp://www.bes.ltd.uk
and put “bronze pump” in the search box. They offer the DAB
VA55/150 but they are significantly more expensive than CI pumps.”
(link)

There
are three types of water conditioner.

There
are the electric/magnetic type. The theory is that calcium ions
have to be set at 60o to each other to bind. The magnetic field
lines them up so they can’t bind to each others. Other people
think they use witchcraft.

The
second type are the phosphate ion conditioners. A small amount
of a phosphate salt is added to the water. This binds
preferentially to the calcium ions. With this type of
conditioner, the calcium stays in the water and so you get
staining from evaporation. Unlike normal scale, this is easily
wiped off.

The
third type is the ion-exchange conditioner which removes the
calcium from the water.

Ion-exchange
is definitely the highest quality solution but it also the most
expensive (by some distance), uses lots of water for the
flushing cycle and you have to keep filling it up
with salt.

For
us, we didn’t think the advantages of ion-exchange over
phosphate salt were sufficient enough for us to stump up the
extra £hundreds.

\

“re
cheap electrically-activated valves, the best value by far is the
Honeywell HR20 (aka rondostat). They are cheaply available in
Germany at about €15-20 each (search ebay.de). Free Software is
available to make them do more stuff and use a wireless interface
if desired. They will drive any valve with a standard 5mm-travel
plunger, as found on TRVs. I have not yet found a cheap electric
mixer valve, although Belimo seem the least extortionate candidate.”
(link)

Some
talk of vented
heat stores being considered a pressured system if using a coil to
heat mains-pressure water; hence it may be necessary to use a PHE to
avoid expensive yearly checks.(link)
“re: pressurised coil in the cylinder. no this doesn’t need to be
serviced every year - there’s a minimum volume requirement of such a
pressurised system from the nanny state to qualify, so cyinder coils
fall under that. Or so I’m led to believe.” (link)

“Our
coil-in-tank is simpler and supplies two showers with ease. “
(link)
Link
to the scale reduction system Richard Owen loves. Richard also
loves the Danfoss wirelss room stats / controllers from BES with
set-back

Feed and Expansion {#feed-and-expansion dir=”ltr”}

“Make
sure that you size the F&E tank properly. Most are designed to cope
with just the heating circuit. If you add a 200 or so litre thermal
store, the potential for expansion increases substantially.

\

If
you are going thermal solar as well, the F&E tank needs to cope with
higher temperatures than usual. E.g. 95 dC instead of 65. Check that
it can cope. Perhaps there will be a market for decent size galvanised
tanks again.

\

Remember
to install a couple of MagnaClean or equivalent filters. One on the
boiler circuit and one on the radiator return to the store so as to
maximise protection.” (ref)

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